It has been an established technology to make a precise inspection of semiconductor devices, etc. in a nondestructive way by means of a scanning electron microscope.
For example, with the advent of a 64-MBit dynamic random access memory (64 MDRAM), etc., the semiconductor devices are realized by means of lines as fine as 0.5 .mu.m or even 0.35 .mu.m. In this case, it is desired that the semiconductor device be inspected correctly by means of a scanning electron microscope.
Methods for realizing precise and correct inspections of a semiconductor device include the method of improvement of the scanning electron microscope itself and the method of improvement of the image data derived on the scanning electron microscope. This invention concerns the latter type of method.
In order to improve the image data derived by a scanning electron microscope, the noise, mainly the thermal noise, has to be suppressed. For this purpose, the number of scans of the scanning electron microscope on the semiconductor device or other specimen as the inspection object is increased in the conventional scheme.
When the scan number of the semiconductor device or other specimen being inspected by the scanning electron microscope is increased, the dose of the primary electrons irradiated on the semiconductor device or other specimen is increased, and the semiconductor device itself may be degraded. In particular, for inspection of a 64 MBit or higher-density DRAM, as the line width and layer thickness are very small inside the semiconductor device, the device may be degraded significantly under irradiation of the excessive dose of the primary electrons in the scanning electron microscope.
Also, as the scan number of the specimen is increased in the scanning electron microscope, the inspection time needed is prolonged, and the inspection efficiency is decreased.